Re: [tcpm] tcp window size

Yoshifumi Nishida <nsd.ietf@gmail.com> Mon, 20 May 2019 19:37 UTC

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From: Yoshifumi Nishida <nsd.ietf@gmail.com>
Date: Mon, 20 May 2019 12:37:19 -0700
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To: Marc <gaardiolor@gmail.com>
Cc: "tcpm@ietf.org Extensions" <tcpm@ietf.org>
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Subject: Re: [tcpm] tcp window size
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Hi Marc,

On Mon, May 20, 2019 at 9:23 AM Marc <gaardiolor@gmail.com>; wrote:

> Hello experts,
>
> I've been trying to find definitive information about tcp window size
> negotiation, and if it exists at all.
>
> Take a browser that downloads a file (receiver) and a webserver (sender).
> If
> - both sender and receiver support window scaling
> - the receiver advertises a TCP winsize of 256KB
> - the sender advertises a window size of 32KB
> - the sender has enough space in its TCP send buffer
> (/proc/sys/net/ipv4/tcp_wmem on linux)
>
> How much 'outstanding unacked data' is the sender allowed to have,
> 32KB or 256KB ?
>

advertised window is receiving buffer size on each side.


> I can't see any logic for it being limited to the window size of the
> sender (32KB), I think it depends on both the receiver winsize and the
> sender TCP Send Buffer Size, but I need to be sure.
>
> Reading https://tools.ietf.org/html/rfc793 also suggests there is no
> such thing like window size 'negotiation' and each end of a TCP
> connection just advertises its own to indicate how much data it can
> receive, independently.
>
> Is that correct ?
>

yep, correct.
--
Yoshi